This invention relates to radially loading the rotor bearings of a limited rotation electomechanical actuator.
Even relatively expensive ball bearings used to hold the ends of the rotor shaft of such an actuator inherently have radial free play. If not adequately controlled, this radial free play can allow the rotor to shift radially causing bearing fretting corrosion and in some instances can make the rotor motion to noisy, typically leading to a catastrophic failure. Various techniques have been attempted to control the free play. Axial preload is normally used with rotating machinery but the resulting added friction makes this method unacceptable to precision oscillating scanners.
In Montagu, U.S. Pat. No. 3,624,574, the bearings are mechanically loaded radially by a flexed torsion bar connected coaxially to one end of the rotor shaft. The rotational stiffness of the torsion bar limits its utility in high-speed applications.
In Brosens, U.S. Pat. No. 4,135,119, incorporated herein by reference, the bearings are proposed to be loaded radially by an imbalanced bias magnetic flux that results from slotting one or both pole faces of the rotor.